The dual challenges of climatic change and depletion of oil reserves presents modern societies with a conundrum. Many of the alternatives to oil derived fuels produce higher carbon emissions, with associated costs to the environment and, if carbon emissions are priced, to the consumer. The early identification and development of solutions to this conundrum will allow for alternative to be introduced in a planned manner, thus avoiding disruptive change. In this application, we propose to explore the use of dimethyl ether (DME) as means of addressing this challenge. DME holds promise as a fuel is that can assist in the transition to a low carbon emissions future. In the short to medium term DME can be produced from natural gas (NG), with well-to-wheel emissions comparable with those of conventional fuels. An attraction of the introduction of DME as a fuel is that the infrastructure and technologies developed for its use now will position societies well for the future. DME is an ideal fuel for a range of stationary and mobile applications. It can be used in place of, or blended with liquefied petroleum gas (LPG), and is an excellent diesel fuel. In each case it produces significantly less pollution upon combustion than its conventional counterpart. Moreover, Dimethyl ether (DME) has been recently proved as a clean fuel because of its wide range of applicability's in industry such as aerosol propellant, in shaving cream, to replace ozone depleting chlorofluorocarbons in refrigerators. It would soon be able to replace conventional diesel fuel because of its thermal efficiencies equal to diesel fuel, high anti knocking property, low NOx emission. Secondly, it does not corrode the metal and less toxic for human beings. So methanol dehydration to DME production is development of an economic process. DME can be synthesized from two ways (1) directly from syngas (mixture of CO and H2) over a hybrid catalyst through a two-step process hence it is energy consuming. Moreover the outcome product stream has lots of byproduct which reduces selectivity of DME. (2) Other process is methanol dehydration to DME through single step process.
The dehydration of methanol to DME is an exothermic process hence it follows a degree of conversion at reaction temperature as soon as possible. From the kinetic point of view, a minimum reaction temperature is required to ensure sufficient reaction rates. Extensive studies have been carried out on methanol dehydration to DME with different type of solid acid catalyst. The solid acid catalyst used for methanol to DME preparation includes gamma alumina (Japanese patent Kokai 1984-16845) silica-alumina (Japanese Patent Kokai 1984-42333) having hydrophilic surface. So as the reaction precedes catalyst get deactivated soon due to rapid blockage of activated site. However γ-alumina delivers high methanol conversion but irreversible deactivation desiccates for its industrial uses. The dehydration process of methanol to DME is acid catalyzed reaction, however, with high acidity of catalyst DME selectivity substantially decreases due to formation of hydrocarbons. Moreover, it is very difficult to precede catalytic dehydration step with weak acidity. This problem can be overcome by synthesis of catalyst with moderate acidity with significantly high surface area.
Reference can be made to the U.S. Pat. No. 8,304,582B2 wherein Zheng Li, et al. provided a one-step catalytic process of dehydration of methanol for the production of DME using silica aluminum phosphate catalyst. But the maximum conversion for methanol reaches to 86.06 at 360° C. and DME selectivity up to 96.78%. But the uses of excess pressure (up to 1500 KPa) reduce the life time of Si—Al—P catalyst.
Reference can be made to U.S. patent US 2011/0065963 A1 by Xiangbo Guo, et al. In their patent application, they claimed Beta-zeolites, and SAPO-molecular sieves catalyst for dehydration of methanol at ≦180-500° C. The main drawback of this process is the relative low conversion of methanol (only 80%). Furthermore, 500° C. is too high for methanol dehydration and at this temp coke deposition will favor rather than methanol dehydration. So life time of the catalyst have to be addressed.
Reference can be made to U.S. Pat. No. 5,750,799A in which Christiaan P. van Dijk and his coworkers disclose a process of DME Production and its recovery from methanol. But, the conversion they have addressed is only 76% whereas in presence of more amount of water it will further decreases.
Reference can be made to the European patent EP1597225 A4 by Jin Hwan Bang et al. in which they developed one step Process for preparing DME from methanol using hydrophobic zeolite having the SiO2/Al2O3 ratio of 20-100. The reaction performed in a temperature ranges 150-350° C. at pressure ranges 1-100 bar and LHSV (liquid hourly space velocity) ranges 0.05-50 h−1 where the outcome yield of DME is 91%. But such a high pressure is not viable for its industrial application, moreover the used of double packed catalyst system (which comprised one hydrophilic solid acid catalyst followed by hydrophobic MFI catalyst) makes the system more and more complex to tune for better conversion and yield.
Reference can be made to the Energy & Fuels 2009, 23, 1896-1900; wherein F. Yaripour et al. reported how phosphorus concentration affects methanol to DME yield over AlPO4 as catalyst. Under the reported process 81.69% DME yield at 300° C. has been achieved with AlPO4 catalyst. But only 81% methanol conversion can be achieved at 300° C.
Reference may also be made to Recent Patents on Catalysis, 2013, 2, 68-81, in which DME synthesis was carried out by two step process using CO and H2 as starting material by copper dispersed on metal oxides. A product selectivity of ≧91% was achieved over CuO, ZnO and Al2O3 in different stoichiometric ratio. But main drawback is to obtain such a high CO conversion (maximum up to 95%) and DME selectivity pressure requirement of the reactor is 60 bar.
Reference may also be made to Fuel Processing Technology 91 (2010) 461-468 where methanol to dimethyl ether was carried out over various commercial mordenite and ion-exchanged catalysts by Moradi and his coworker. A conversion of 84.1 was obtained with 100% DME selectivity but GHSV and to achieve the conversion is too low.
Reference can also be made to US patent 20120220804A1 by Peter Mitschke et al. have reported a process for DME synthesis from crude methanol dehydration. However the crude methanol dehydration is an economic process but on increasing the content of carbonyl compound greater than 50 wt-ppm harmful trace components will appear in DME product.